Patent Document 1 relates to control of charging/discharging of a plurality of secondary batteries. Patent Document 1 discloses that orders of charging priority and orders of discharging priority are given to the plurality of secondary batteries (secondary battery modules 7a and 7b) (paragraph 0090, etc.), charging power is allocated to the secondary batteries in descending manner of order of charging priority and discharging power is allocated to the secondary batteries in descending manner of order of discharging priority (paragraph 0107), the charging/discharging power is adjusted according to an amount, correlated with internal resistance (paragraph 0080, etc.) and so on.